24 INTRODrCTION. 



tinguish ; and in some cases tlie whole embryo will elude the most careful 

 search until the seeds begin to germinate. 



Although the embryo hes loose within the seed, it is generally in some 

 determinate position with respect to the seed or to the wliole fruit. This 

 position is described by stating the direction of the radicle, which is said 

 to be 



superior, if pointuig towards the summit of \h.e fruit. 



inferior, if pointing towards the base of \\iq fruit. 



next the hilum, if pointing towards the hilum, or base of the seed,. 



§ 15. Accessory Organs. 



Under this name are included, in many elementary works, various ex- 

 ternal parts of plants wliich do not appear to act any essential part either in 

 the vegetation or reproduction of the plant. They may be classed under four 

 heads, Teiidrih and Hooks, Thorns and Prickles, Hairs, and Glands. 



Tendrils are usually abortive petioles, or abortive j)eduncles, or sometimes 

 abortive ends of branches. They are simple, or more frequently branched, 

 flexible, and coil more or less firmly rovxnd any objects within their reach in 

 order to support the plant to which they belong. Hooks are the same thing, 

 only of a firmer consistence, not branched, and only hooked at the extremity. 

 Thorns and Prickles have been fancifully called the weapons of plants. 

 A Thorn is the strongly pointed extremity of a branch, or abortive petiole, or 

 abortive peduncle. A Prickle is a sharply pointed excrescence from the 

 epidermis, or skin, and is usually produced on a branch, on the petiole, or 

 veins of a leaf, or on a peduncle. When the vein of a leaf projects beyond 

 the margin with a sharp point, it is called also a prickle, not a thorn. A 

 plant is spinous if it has thorns, aculeate if it has prickles. 



Hairs, in the general sense, or the indumentum (or clothing) of a plant in- 

 clude all those productions of the epidermis which have, by a more or less 

 appropriate comparison, been termed bristles, hairs, doivn, cotton, or wool. 

 They appear sometimes to afford some kind of protection against meteo- 

 rological vicissitudes, occasionally to assist in the disjjcrsion of pollen, but, 

 generally speaking, to have no vei-y evident use. 

 The epidermis, or the surface of an organ, is 



smooth, when without any protuberance whatever. 



glabrotis, when without any hairs of any kind. 



striate, when marked with parallel longitudinal lines, either slightly 

 raised, or merely discoloured. 



furrotoed, or ribbed, when the parallel lines are more distinctly raised. 



viscous, viscid, or glutinous, when covered with a sticky or clammy 

 exudation. 



tuberculate, or ivarted, when covered with minute protuberances, com- 

 pared to warts. 



muricate, when the protuberances are more raised and pointed, yet not 

 slender enough to be called bristles, nor large enough to be called prickles. 



setose, or bristly, when bearing stiff erect hairs. 



glandular-setose, when the setae or bristles terminate in a minute 

 resinous head or drop. Those who specially study roses and brambles, limit, 

 in that case, the meaning of setm to such as are glandular. 



glochidiate, when the setae are hooked at the top. 



pilose, when the surface is thinly scattered with rather long simple 

 hairs. 



hispid, when more thickly covered with rather stiff hairs. 



